1. Technical Field
The present invention relates to a liquid ejecting head that ejects ink through a nozzle, and a liquid ejecting apparatus incorporated with the liquid ejecting head.
2. Related Art
The liquid ejecting apparatus includes a liquid ejecting head, and is designed to eject various types of liquid from the ejecting head. An image recording apparatus, such as an ink jet printer or an ink jet plotter, is a typical example of the liquid ejecting apparatus, however recently the liquid ejecting head has come to be increasingly applied to various manufacturing apparatuses, because of the benefit in that a minute amount of liquid can be accurately shot onto a predetermined position. Such a liquid ejecting head is employed, for example, in display manufacturing apparatuses for manufacturing color filters for LCDs, electrode forming apparatuses for manufacturing electrodes for organic electroluminescence (EL) displays or field emission displays (FED), and chip manufacturing apparatuses for manufacturing biochips (biochemical elements). The recording head in the image recording apparatus ejects liquid ink, a color material ejecting head in the display manufacturing apparatus ejects solutions of color materials of red (R), green (G), and blue (B). An electrode material ejecting head in the electrode forming apparatus ejects a liquid electrode material, and a bioorganic ejecting head in the chip manufacturing apparatus ejects a solution of a bioorganic substance.
The liquid ejecting heads thus far developed include those having a pressure chamber substrate on which a pressure chamber is formed, a nozzle substrate including nozzle holes, and a communication substrate provided between the pressure chamber substrate and the nozzle substrate (for example as disclosed in JP-A-8-258258). These substrates are bonded together with an adhesive. The communication substrate includes a communication via communicating between the pressure chamber and the nozzles. The liquid ejecting head of such a type is configured to drive a piezoelectric element to change the pressure on the liquid in the pressure chamber, and thus ejects the liquid in the pressure chamber through the communication via out of the nozzle.
However, a part of the adhesive may be squeezed out from between the communication substrate and the nozzle substrate upon bonding these substrates together, and the adhesive that has been squeezed out may proceed upward (toward the pressure chamber) along a portion corresponding to the interior angle of the communication via, owing to a capillary effect. In such a case, after the communication substrate and the nozzle substrate are bonded together the adhesive that has cured remains on the inner wall of the communication via. In particular, the leading end portion of the adhesive that remains on the inner wall on the side of the central portion of the pressure chamber is prone to intrude in the pressure chamber, and the end portion of the adhesive may be scraped off by the liquid flowing from the pressure chamber toward the nozzle. In case that the adhesive thus scraped off sticks out from the nozzle, the ejection characteristics of the liquid droplet (amount, flying speed, and flying direction of the liquid droplet) ejected from the nozzle fluctuate, and besides the nozzle is prone to be clogged with the adhesive.
Accordingly, a remedy has been proposed as shown in FIGS. 8A and 8B, in which a sloped surface 96 is formed on one side of the inner wall of the communication via 92 (on the side of the central portion of the pressure chamber), so as to restrict the adhesive from proceeding further. More specifically, the communication via 92 in the communication substrate 90 is formed so as to include a first flow path section 93 on the side of the pressure chamber, a second flow path section 94 on the side of the nozzle 98 wider than the first flow path section 93, and an intermediate flow path section 95 connecting between the first flow path section 93 and the second flow path section 94 and including the sloped surface 96. With such a configuration, even though the adhesive proceeds upward along the inner wall of the second flow path section 94 upon bonding the communication substrate 90 and the nozzle substrate 91 together, the sloped surface 96 of the intermediate flow path section 95 serves to suppress the adhesive from proceeding further. As a result, the adhesive can be prevented from being scraped off, and therefore the fluctuation of the ejection characteristics of the liquid droplet ejected from the nozzle 98, as well as the clogging of the nozzle 98 can be prevented.
With the liquid ejecting head that includes the communication via 92 configured as above, however, an air bubble often resides in the communication via 92 in a region below the sloped surface 96, when the liquid is first loaded in the flow path (at the time of initial loading of the liquid). To be more detailed, when the liquid is supplied from the pressure chamber in the initial loading of the liquid, the liquid L proceeds downward from the upper portion of the first flow path section 93, as shown in FIG. 8A. At this point, the surface of the liquid L assumes a shape having an arcuate cross-section, because the peripheral edge of the liquid surface proceeds along the inner wall of the communication via 92 in contact therewith at a certain contact angle. Here, FIGS. 8A and 8B and FIGS. 9A to 9C represent a case where the contact angle of the liquid L with respect to the inner wall of the communication via 92 is smaller than 90 degrees, in other words where the communication substrate 90 has affinity with liquid. When a portion of the peripheral edge of the liquid surface reaches the sloped surface 96 of the intermediate flow path section 95, the liquid L turns the moving direction in an oblique direction as shown in FIG. 8B. Then the liquid L moves obliquely downward until the opposite edge of the liquid surface reaches the lower end of the second flow path section 94, i.e., the nozzle substrate 91, as shown in FIG. 9A. When the opposite edge of the liquid surface reaches the nozzle substrate 91, the opposite edge starts to move in the horizontal direction along the nozzle substrate 91 as shown in FIG. 9B and therefore the liquid L moves in a generally horizontal direction. When the opposite edge of the liquid surface reaches the nozzle 98, the liquid L is introduced into the nozzle 98 and thus the initial loading of the liquid L is completed. At this point, the communication via 92 is not entirely filled with the liquid L, and an air bubble b remains in a region below the sloped surface 96, as shown in FIG. 9C. The air bubble b thus formed in the communication via 92 often degrades the ink ejection performance.